More precisely, the present invention relates to a personal activity monitor (also called ‘activity monitoring device’ or ‘personal activity tracker’ or the like), that can be worn by its user on various positions, for example at the wrist, or at the waist, or in various other locations where it can be coupled to the user's body. More specifically, the present invention relates to a device having small dimensions and low weight, and which can be associated to the user's body via various coupling means, for instance associated to the wrist via a wrist strap, or associated to the waist via a belt clip and a belt, or associated to the chest via a clip on a shirt, or simply carried in a pocket of a cloth. Advantageously to the benefit of the user, a single device can be associated to the user's body in different manners using various attachments or coupling means; it is thus very flexible and convenient for the user who can wear the device nearly at all times regardless of the type of activity (bath/shower/swimming/sleeping not excluded). Nonetheless, the configuration when the user does not wear the device can sometimes occur and has to be contemplated.
Also the purpose of this monitoring device is to follow all the activities of the user as much as possible, various active physical activities, user's rest conditions, including user's sleep condition.
It is therefore required for the activity monitoring device to recognize both the current position of the device on the body, and also recognizes the type of activity undertaken by the user.
EP-A-2255209 discloses such a personal activity monitoring device. However, the method to identify the current device position relies on the one hand on complicated signal signatures and on the other hand does not consider rest and sleep activities.
Therefore, it arose a need to be able to identify more easily the current device position, in particular the wrist position and also to identify a user's sleep state, condition that has to be distinguished from a case when the device is not worn by the user.